Note: Descriptions are shown in the official language in which they were submitted.
11C~(~319
Oil Return System and Method
This invention relates to refrigeration systems in ge~eral, and in
particular to an oil return system for refrigeration compresæors
employed in refrigeration systems wherein the compressor is
continuously driven regardless of the refrigeration load on the
system.
There are many refrigeration systems wherein the compressor
employed in the system runs continuously irrespective of the
refrigeration load on the system. For example, in transportation
refrigeration systems, such as those used on buses or similar
vehicles, the compressor is directly connected to the vehicle's
engine and will run continuously as long as the engine is
operating. Operation of the compressor will thus continue
irrespective of the refrigeration load on the refrigeration
system.
In continuously operating refrigeration systems, there are various
types of capacity control arrangements which may be employed for
varying the refrigeration load handling capabilities of the system
at varying load conditions. In one such capacity control
arrangement, a valve is interposed in the refrigeration suction
line upstream of the refrigeration compressor to control the flow
of the refrigerant gas to the compressor. The suction gas control
valve varies the refrigerant flow in accordance with the load on
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the refrigeration system; at relatively high loads, the valve
opens to increase the refrigerant flow to the compressor, whereas
at relatively low load conditions the valve closes to decrease the
flow of the gas to the compressor.
During operation of the compressor, relatively small quantities of
lubricating oil will bypass the piston rings and be discharged
into a discharge gas manifold such as a discharge gas cavity
formed in the cylinder head of the compressor. During normal
operating conditions, any lubricating oil discharged from the
compressor cylinder will be drawn with the relatively high
velocity, high mass flow refrigerant gas through the refrigeration
system and return to the lubricating oil sump of the compressor.
However, at relatively low mass flow conditions which occur
generally at relatively low refrigeration loads, there is an
insufficient mass of refrigerant gas to carry the generally
heavier lubricating oil therewith. Thus, the oil flowing from the
cylinder into the discharge gas cavity will accumulate
therewithin. Continuous operation of the compressor for prolonged
periods of time at relatively low mass flow conditions, such as
those encountered under reduced refrigeration loads, will result
in an accumualtion of substantially all of the lubricating oil in
the discharge cavity thereby rendering the compressor subject to
lubricating oil starvation. Oil starvation of the co~pressor may
result in damage to bearings and other moving parts of the
compressor requiring lubrication. In addition, if the system were
to stop, the accumulated oil in the digcharge cavity of the
compressor may drain into the compressor's cylinders. Upon
restarting, the incompressible slugs of oil in the cylinders may
cause damage to the compressor valves, pistons, rods, and/or
compressor gaskets. Thus, as is obvious, it is essential that the
accumulation of the refrigerant oil at relatively low mass flow
rates be eliminated.
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In view of the above, the present invention relates
to a refrigeration system including a refrigerant compressox
having an oil return system for returni~ng oil acc~nulated
within a first port.~on of tfie compressor operating at .~
refrigerant discharge pressure to a second portion of the ~;
compressor operating at s-u~stantially refrigerant suction
pressure. Conduit means connects the first por~ion of the :;~
compressor with the second portion o~ the comp.ressor for
delivering lubricating oil accumulated within the first
portion to the second portion. Normally closed valve means
is interposed in the condu;t means for controlling flow of ~:
lubricating oil through the conduit means. The valve is
opened in response to a sensed operating parameter of the
refrigeration system with the parameter being indicative of
the flow rate of the refrigerant gas to the compressor.
In accordance with a broad aspect, the i.nvention
relates to an oil return system for a refrigerant compressor
for returning oil accumulated within a fixst portion of the
col-npressor operating at refrigerant discharge pressure to a
2~0 second portlon of the compressor operatlng at substantially
refrigerant suction pressure comprising conduit means ..
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connecting the first portion of the compressor with the
second portion of the compressor for delivering lubricating
oil accumulated withi]l said first portion to said second
portion; and normall~ closed valve means interposed in
said conduit means ~or controlling the flow of lubricating
oil througll said conduit means including sensing means for
sensing the magnitude of the pressure ln said second portion
of the compressor and operating means connected to said
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sensing means ~or opening said val~e means when the sensed
pressure decreases below a predetermined level for enabling
the oil to flow through said conduit means from said first
portion to said second portion.
In accordance with another broad aspect, the
invention relates to a refrigeration system including a
refrigerant compressor having a first portion operating at
refrigerant gas suction pressure and a second portion
operating at refrigerant gas discharge pressure comprising
first means for controlling the flow rate of refrigerant
gas to said compressor; conduit means connecting the second
portion of the compressor with the first portion of the
compressor for delivering lubricating oil accumulated within
sa.d second portion to said first portion; and normally
closed valve means interposed in said conduit means for
controlling flow of oil through said conduit means including
means to sense an operating parameter of said system
in-licative of the flow rate of said refrigerant as controlled
by said first means and operating means connected to said
sensing means for opening said valve means when the flow rate
of said refrigerant has decreased below a predetermined
level for enabling the oil to flow throush said conduit
means from said secol-d portic?n to sl-3id first portion.
In accordance with a ful-ti~er lroad aspect, the
invelltion relates to a met}-od of l-etlll-ni71g refrigerant
co~ re-.sor 1l~ricati7-~g oil accl7m.ll1.3t(d in a first portion of
the co5ll;?l-cssor c~i~erati r7g at re ri~1er1llt discharge pressure
to a sec o~l(l pOI-t i..sl of the cos~!5>rc~;sc-l- operating substantially
~3t refl-igerant suction pressure, tl)e oi l i~eing accumu1ated
in the first ~ortion w}len the flo~.~ r.~t-~ of tshe refrigerdnt
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to the compressor is reduced ~eIo~ a predetermined level
comprising the steps o~ sensing an operating parameter
indicati~e o~ the flow rate of refrigerant to the compressor;
and communicating the first portion of the compressor with
the second portion of the compressor when the sensed
parameter indicates the flow rate of refrigerant has
decreased below the predetermined level for enabling
refrigerant accumulated in the first portion to flow to
said second portion.
This invention will now be described by way o~
example, with reference to the accompanying drawing in which:
Figure 1 schematically illustrates a refrigeration
system of a type employing the present invention and includes
a ~artial sectional view of a refrigerant compressor; and
Figure 2 is a partial sectional view of a valve
employed in the system disclosed in Figure 1. -
Referring now to the drawing, there is disclosed
a refrigeration system 10 including the invention herein
disclosed. Refrigeration system 10 includes a refrigerant
compressor 12 connected through a discharge line 14 to a
condenser 16~ High pressure refrigerant gas delivered
from compressor 12 is transformed into a high pressure
liquid refrigerant in condenser 16 by passing in heat
transfer relation with a low temperature medium, as
for example air. T]~e high pressure liquid refrigerant
is deli~exed from con(.e3lser 16 through conduit 18,
expansion de~ ~e 2~, to a reIrigerant evapordtor 22.
Expansion de~ice ~0 is illustrated as
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being a thermal expansion valve of a type well known to those
skilled in the art; however, the valve may be replaced by other
suitable expansion devices as for example capillary tubes. The
pressure of the liquid refrigerant is reduced as it passes through
expansion device 20 resulting in the generation of a relatively
low pressure mixture of liquid and vaporous refrigerant. This
mixture is passed through evaporator 22 wherein the mixture is
totally vaporized by absorbing heat from the medium to be cooled,
as for example air. The low pressure vaporous refrigerant passes
through conduit 24, throttling valve 26 and thence returns to a
suction manifold 41 of compressor 12. Valve 26 modulates the flow
of refrigerant to the suction side of the compressor in accordance
with the refrigeration load on system 10. Valve 26 operates to
reduce the flow of refrigerant as the load on system 10 decreases
and conversely increases the flow of refrigerant as the load on
system 10 rises. Valve 26 may be controlled manually or
automatically via suitable means (not shown) responsive to changes
in the refrigeration load on system 10. It should be understood,
valve 26 may be replaced by suitable alternate means for
controlling the mass flow of refrigerant through the system in
accordance with the refrigeration load thereon. The system
hereinabove described is a conventional mechanical refrigeration
system of a type well known to those skilled in the art.
Compressor 12 generally includes one or more cylinders 36 having
pistonfi 37 connected by connecting rods 39 to an eccentric portion
of crankshaft 38. Rotation of crankshaft 38 causes reciprocating
movement of pistons 37 within cylinders 36. The compressor
further includes a cylinder block 30 defining the cylinders of
compressor 12. One or more cylinder heads 32 are suitably
attached to cylinder block 30. Each cylinder head 32 defines a
suction chamber 44 and a discharge chamber 46. Each suction
chamber 44 is in co~munication with suction manifold 41. Each
discharge chamber 46 is in communication with discharge manifold
43. A valve plate 42 is interposed between cylinder head 32 and
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cylinder 36; valve plate 42 includes suitable suction and
discharge valves (not shown) for controlling the flow of gas from
suction chamber 44 to the cylinder and thence from the cylinder,
subsequent to the compression of the gas therewithin, to discharge
chamber 46. One or more valves 28, to be more fully described
hereinafter, are provided with each valve having a first conduit
50 in communication with the suction chamber 44 and a second
conduit 48 in communication with discharge chamber 46.
Cylinder block 30 defines an oil sump 43 in which a body of oil 40
is stored. The oil is employed for lubricating the various moving
parts of compressor 12. A check valve 52 is provided between
suction manifold 41 and oil sump 43.
Referring now to Figure 2, there is disclosed a detailed view of
valve 28. Valve 28 includes a body 51 in which a bellows 56 is
suitably mounted. A spring 58 provides a first force acting on
one side of the bellows. A suitable adjusting screw 54 controls
the force generated by the spring. Valve 28 further includes a U-
shaped bracket member 60 suitably attached to the bellows 56 and
movable therewith. A needle valve 62 is affixed to one leg of U-
shaped bracket 60; bellows 56 thus controls movement of valve 62
relative to valve seat 64 provided at one end of conduit 48. When
valve 62 is unseated with respect to seat 64, oil will flow
through conduit 48 into chamber 61 and thence into conduit 50.
The flow of oil will occur due to the pressure differential
between chambers 46 and 44. Conduit 50 delivers refrigerant gas
at suction pressure to a chamber 61 for generating a force on
bellows 56 in opposition to the force generated by spring 58.
In operation, as noted previously, valve 26 regulates the flow of
refrigerant directly in accordance with the refrigeration load on
system 10. Valve 26 is particularly employed in refrigeration
systems wherein the refrigeration compressor operates continuously
irrespective of the refrigeration load on the system. During
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operation of the compressor, relatively small quantities of
lubricating oil will bypass the piston rings and flow with the
refri8erant gas discharged from the cylinders into discharge
chambers 46. It has been found that as the flow rate of the
refrigerant is reduced, the oil will stagnate within each
discharge chamber 46. At higher flow rates, the high mass flow,
high velocity refrigerant discharged into chamber 46 will carry
the lubricating oil through the refrigeration system and thence
return the bypassed lubricating oil to the suction side of the
compressor. The oil is separated from the refrigerant and
returned to the oil sump. However, at low mass flow conditions,
such as those that occur at relatively low refrigeration loads,
the reduced flow of refrigerant is not able to carry the bypassed
lubricating oil through the system and therefore the oil
accumulates within each discharge chamber 46. As is evident, the
accumulation of oil within the discharge chambers, if continued
for a relatively prolonged period of time, may result in oil
starvation of the compressor. In addition, if the compressor were
to be stopped the accumulated oil in discharge chambers 46 may
drain into cylinders 36. Upon restarting, the incompressible
slUg8 of oil in the cylinders may cause damage to the valves,
pistons and other components of the compressor. In view of the
foregoing, it is necessary that the accumulation of oil be
prevented.
To schieve the above desiderata, valve 28 is employed.
Refrigerant gas at suction pressure is delivered from chamber 44
through conduit 50 into chamber 61 of valve 28. As the pressure
and flow rate of the refrigerant decreases, due to a decreased
refigeration load on system 10, the pressure in chamber 61 will
concurrently decrease. The force generated by spring 58 acting on
the opposed side of bellows 56 will soon exceed the force
generated within chamber 61 by the suction pressure of the
refrigerant gas, causing U-shaped bracket 60 to move to the right
as viewed in ~igure 2. Movement of the bracket as described
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results in valve 62 moving away from and thereby opening valve
seat 64 to permit flow through conduit 48.
Conduit 48 is in communication with discharge chamber 46. Thus,
oil accumulated within discharge chamber 46 will flow through the
now open conduit 48 into chamber 61. The oil contained within
chamber 61 will flow, as it is at a relatively higher pressure
than the refrigerant gas at suction pressure downwardly through
conduit S0 into suction chamber 44 and thence into suction
manifold 41 through port 66. The lubricating oil will accumulate
within suction manifold 41 until the pressure thereof opens
normally closed check valve 52 thereby permitting the lubricating
oil to pass from suction manifold 41 into lubricating oil sump 43.
Thus, at low mass flow conditions, normally closed valve 62 is
opened, communicating chamber 46 with chamber 44 for enabling
lubricating oil to flow from chamber 46 to chamber 44. Valve 62
is opened through the sensed occurrence of a parameter in the
system indicative of low mass flow conditions.
As the load on the sytem increases, the refrigerant gas pressure
of the gas returning to manifold 41 and thence into suction
chamber 44 will likewise increase due to the opening of valve 26.
The subsequent increase in pressure within chamber 61 of valve 28
will cause U-shaped member 60 to move to the left as viewed in
Figure 2, placing valve 62 in its seated position with respect to
seat 64. The movement of valve 62 into its seated position,
terminates flow of oil through conduit 48. Any oil thereafter
accumulated within chamber 46 will move through the refrigeration
system 10 due to the hiBh mass flow, high velocity conditions of
the refrigerant gas.
The arrangement herein disclosed provides a system which prevents
oil starvation of a refrigerant compressor operating at low
suction pressure, low mass flow conditions. ~he arrangment is
directly sensitive tG the occurrence of the low refrigerant mass
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flow conditions which heretofore have caused problems as explained
above.
While a preferred embodiment of the present invention has been
described and illustrated, the invention should not be limited
thereto but may be otherwise embodied within the scope of the
following claims.
